Effect Of The Sink To Source Ratio On Photosynthesis And Carbohydrate Metabolism In Peach Trees (Prunus Persica)

Effect of fruiting (control) and defruting on photosynthesis and carbohydrate metabolism was studied on five-year-old peach trees(Prunus persica(L.) Batsch.) in the field. Net photosynthesis, transpiration, stomatal conductance, leaf temperature, non-structural carbohydrate content and activities of related key metabolic enzymes were measured during fruit stone hardening and fruit final rapid growth. The main results were obtained as follows:1. Net photosynthesis in peach leaves for defruiting treatment was significantly lower than that for fruiting in a day during fruit stone hardening and fruit final rapid growth. However, the diurnal variation of net photosynthesis in peach leaves for both fruiting and defruiting treatment had a similar trend, namely single-peak curve, and the peak generally appeared before twelve o'clock. Defruiting treatment also reduced stomatal conductance significantly, especially in midday. A similar diurnal variation of stomatal conductance to that of net photosynthesis was observed in peach leaves for both fruiting and defruiting treatment. Defruiting treatment tend to increase leaf temperature 0.7-2.1 C and decrease transpiration rate of leaves. However, substomatal CO2 in peach leaves had no significant difference between fruiting and defruiting during fruit stone hardening and fruit final rapid growth.2. Defruiting increased significantly sorbitol and starch contents in peach leaves during fruit stone hardening, but defruiting did not influence sucrose, fructose and glucose contents in peach leaves. However, sorbitol, starch, sucrose, fructose and glucose contents had no different between fruiting and defruiting treatment during fruit final rapid growth. Only sorbitol and fructose among them had significant negative correlation with net photosynthesis during fruit stone hardening and fruit final rapid growth.3. Defruting usually did not influence the activities of related enzymes to non-structural carbohydrate metabolism, including aldose-6-phosphate reductase(A6PR),sorbitol dehydrogenase(SDH), sucrose synthase(SS), sucrose phosphate synthase(SPS), acid invertase(AI), neutral invertase(Nl), amylase and ADPG pryophosphorylase(ADPGPPase).